LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andi Kleen <ak@linux.intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Cannon Matthews <cannonmatthews@google.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	David Rientjes <rientjes@google.com>,
	Greg Thelen <gthelen@google.com>, Salman Qazi <sqazi@google.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH] mm: clear 1G pages with streaming stores on x86
Date: Mon, 9 Mar 2020 08:38:31 -0700	[thread overview]
Message-ID: <20200309153831.GK1454533@tassilo.jf.intel.com> (raw)
In-Reply-To: <20200309090630.GC8447@dhcp22.suse.cz>


> Gigantic huge pages are a bit different. They are much less dynamic from
> the usage POV in my experience. Micro-optimizations for the first access
> tends to not matter at all as it is usually pre-allocation scenario. On
> the other hand, speeding up the initialization sounds like a good thing
> in general. It will be a single time benefit but if the additional code
> is not hard to maintain then I would be inclined to take it even with
> "artificial" numbers state above. There really shouldn't be other downsides
> except for the code maintenance, right?

There's a cautious tale of the old crappy RAID5 XOR assembler functions which
were optimized a long time ago for the Pentium1, and stayed around,
even though the compiler could actually do a better job.

String instructions are constantly improving in performance (Broadwell is
very old at this point) Most likely over time (and maybe even today
on newer CPUs) you would need much more sophisticated unrolled MOVNTI variants
(or maybe even AVX-*) to be competitive.

The best clear functions may also be different for different CPU
generations.

Using the string instructions has the advantage that all of this is abstracted
from the kernel.

-Andi

  parent reply	other threads:[~2020-03-09 15:38 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-07  1:03 Cannon Matthews
2020-03-07 22:06 ` Andrew Morton
2020-03-09  0:08 ` Kirill A. Shutemov
2020-03-09  9:06   ` Michal Hocko
2020-03-09  9:35     ` Kirill A. Shutemov
2020-03-09 11:36     ` Kirill A. Shutemov
2020-03-09 12:26       ` Michal Hocko
2020-03-09 18:01         ` Mike Kravetz
2020-03-09 15:38     ` Andi Kleen [this message]
2020-03-09 18:37       ` Matthew Wilcox
2020-03-11  0:21         ` Cannon Matthews
2020-03-11  0:54           ` Kirill A. Shutemov
2020-03-11  3:35             ` Arvind Sankar
2020-03-11  8:16               ` Kirill A. Shutemov
2020-03-11 18:32                 ` Arvind Sankar
2020-03-11 20:32                   ` Arvind Sankar
2020-03-12  0:52                     ` Kirill A. Shutemov
2020-03-31  0:40                   ` Elliott, Robert (Servers)
2020-03-16 10:18             ` Michal Hocko
2020-03-16 12:19               ` Kirill A. Shutemov
2020-03-26 19:46                 ` Matthew Wilcox
2020-03-11 15:07       ` David Laight
2020-03-09 15:33   ` Andi Kleen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200309153831.GK1454533@tassilo.jf.intel.com \
    --to=ak@linux.intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=cannonmatthews@google.com \
    --cc=gthelen@google.com \
    --cc=kirill@shutemov.name \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@kernel.org \
    --cc=mike.kravetz@oracle.com \
    --cc=rientjes@google.com \
    --cc=sqazi@google.com \
    --cc=willy@infradead.org \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH] mm: clear 1G pages with streaming stores on x86' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).